Deprecate `false` as the way to halt AM validation callbacks

Before this commit, returning `false` in an ActiveModel validation
callback such as `before_validation` would halt the callback chain.

After this commit, the behavior is deprecated: will still work until
the next release of Rails but will also display a deprecation warning.

The preferred way to halt a callback chain is to explicitly `throw(:abort)`.

1 files changed, 17 insertions, 3 deletions

diff --git a/activemodel/test/cases/validations/callbacks_test.rb b/activemodel/test/cases/validations/callbacks_test.rb
index 5d6d48b824..4b0dd58efb 100644
--- a/activemodel/test/cases/validations/callbacks_test.rb
+++ b/activemodel/test/cases/validations/callbacks_test.rb
@@ -30,11 +30,16 @@ class DogWithTwoValidators < Dog
   before_validation { self.history << 'before_validation_marker2' }
 end
 
-class DogBeforeValidatorReturningFalse < Dog
+class DogDeprecatedBeforeValidatorReturningFalse < Dog
   before_validation { false }
   before_validation { self.history << 'before_validation_marker2' }
 end
 
+class DogBeforeValidatorThrowingAbort < Dog
+  before_validation { throw :abort }
+  before_validation { self.history << 'before_validation_marker2' }
+end
+
 class DogAfterValidatorReturningFalse < Dog
   after_validation { false }
   after_validation { self.history << 'after_validation_marker' }
@@ -86,13 +91,22 @@ class CallbacksWithMethodNamesShouldBeCalled < ActiveModel::TestCase
     assert_equal ['before_validation_marker1', 'before_validation_marker2'], d.history
   end
 
-  def test_further_callbacks_should_not_be_called_if_before_validation_returns_false
-    d = DogBeforeValidatorReturningFalse.new
+  def test_further_callbacks_should_not_be_called_if_before_validation_throws_abort
+    d = DogBeforeValidatorThrowingAbort.new
     output = d.valid?
     assert_equal [], d.history
     assert_equal false, output
   end
 
+  def test_deprecated_further_callbacks_should_not_be_called_if_before_validation_returns_false
+    d = DogDeprecatedBeforeValidatorReturningFalse.new
+    assert_deprecated do
+      output = d.valid?
+      assert_equal [], d.history
+      assert_equal false, output
+    end
+  end
+
   def test_further_callbacks_should_be_called_if_after_validation_returns_false
     d = DogAfterValidatorReturningFalse.new
     d.valid?